This study is designed to identify those chronic schizophrenic patients who might be especially appropriate candidates for chronic dopamine agonist treatment. Using a crossover random order design, schizophrenic patients are given a single oral dose of amphetamine. Patients are "protected" from possible exacerbation of their psychosis by ongoing treatment with haloperidol. We hypothesize that the deficit symptoms of schizophrenia may be a reflection of cortical dopaminergic failure. Since cortical dopamine receptors are mostly of the D1 subtype and mesolimbic dopaminergic neurones are of the D2 subtype, we hypothesize that amphetamine, a non-specific dopamine indirector agonist given to a person taking the relatively specific D2 blocking agent haloperidol might enhance D1 function. Six of 21 patients were found to be better on the amphetamine day compared to the placebo day. These six had in common greater ventricular to brain ratio and greater enhancement of blink rate compared to the non responsive group. Studies with chronic administration are in progress.